Temperature sensing device in an integrated circuit

ABSTRACT

A temperature sensing device can be embedded in a memory circuit in order to sense the temperature of the memory circuit. One oscillator generates a temperature variable signal that increases frequency as the temperature of the oscillator increases and decreases frequency when the temperature of the oscillator decreases. A temperature invariant oscillator generates a fixed width signal that is controlled by an oscillator read logic and indicates a temperature sense cycle. An n-bit counter is clocked by the temperature variable signal while the fixed width signal enables/inhibits the counter. The faster the counter counts, the larger the count value at the end of the sense cycle indicated by the fixed width signal. A larger count value indicates a warmer temperature. A smaller count value indicates a colder temperature.

RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.10/613,236, titled “TEMPERATURE SENSING DEVICE IN AN INTEGRATEDCIRCUIT,” filed Jul. 3, 2003, now U.S. Pat. No. 7,034,507 (allowed)which is commonly assigned and incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to oscillators and in particularthe present invention relates to variable rate oscillators havingtemperature variable frequencies.

BACKGROUND OF THE INVENTION

It is sometime desirable to know the internal temperature of integratedcircuits. For example, dynamic random access memory (DRAM) devicesrequire periodic refresh cycles in order to maintain the integrity ofthe data stored in the memory. The temperature of the memory deviceaffects the frequency at which the memory device needs to be refreshed.As the device heats up, the cells lose their ability to hold a chargedue to current leakage. Therefore, the warmer the device the more oftenit has to be refreshed.

Designers typically take into account the worst case requirement forrefreshing a DRAM and design the memory to refresh at a fixed rateconsistent with the maximum operating temperature of the part. However,the faster refresh rate is not required when the device is operating ata cooler temperature, thus wasting power. It would therefore bebeneficial to be able to determine the memory device's internaltemperature in order to adjust the refresh rate in response to changingtemperature. In a battery powered electronic device, a smaller powerrequirement could translate into either a smaller battery or longerbattery life.

Additionally, some battery powered electronic devices use ambient anddevice temperature readings to monitor system heating during batterycharging. Such devices typically require at least one externaltemperature sensor that adds to the weight and expense of the electronicdevice. In a market where profit margins are small and size/weight mightdetermine marketing advantage, a less expensive and smaller device ismore desirable.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art fora temperature sensing device that can be used by both an integratedcircuit and any peripheral circuitry.

SUMMARY

The above-mentioned problems with memory testing and other problems areaddressed by the present invention and will be understood by reading andstudying the following specification.

The embodiments of the present invention encompass a temperature sensingdevice. The device includes a temperature variant oscillator thatgenerates a variable rate signal. The frequency of the variable ratesignal varies in response to a temperature of the device. A temperatureinvariant oscillator generates a fixed width signal that indicates asense cycle. A counter generates an n-bit count value in response to thevariable rate signal and the fixed rate signal. The n-bit count valueindicates the temperature.

In one embodiment, the variable rate signal is a clocking signal to thecounter and the fixed width signal is used to enable/disable thecounter. While the counter is enabled, the faster the variable ratesignal clocks the counter, the larger the count that occurs during thesense cycle. The larger count indicates a warmer temperature. Thesmaller the count, the colder the indicated temperature.

Further embodiments of the invention include methods and apparatus ofvarying scope.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of one embodiment of a temperature sensingdevice of the present invention.

FIG. 2 shows timing diagram in accordance with the embodiment of FIG. 1.

FIG. 3 shows a graphical representation of the temperature of anintegrated circuit versus the time period of the temperature compensatedrefresh oscillator in accordance with the embodiment of FIG. 1.

FIG. 4 shows a block diagram of one embodiment of a memory device havingan embedded temperature sensing device in accordance with FIG. 1.

FIG. 5 shows a block diagram of one embodiment of an electronic devicehaving a memory device in accordance with the embodiment of FIG. 4.

FIG. 6 shows a flow chart of one embodiment of a memory read cycleenabling an external system to read the temperature sensing device ofthe present invention.

FIG. 7 shows a flow chart of one embodiment of a temperature sensingmethod of the present invention.

DETAILED DESCRIPTION

In the following detailed description of the invention, reference ismade to the accompanying drawings that form a part hereof, and in whichis shown, by way of illustration, specific embodiments in which theinvention may be practiced. In the drawings, like numerals describesubstantially similar components throughout the several views. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention. Other embodiments may be utilizedand structural, logical, and electrical changes may be made withoutdeparting from the scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims and equivalents thereof.

FIG. 1 illustrates a block diagram of one embodiment of a temperaturesensing device 100 of the present invention. An n-bit counter 101generates a count that indicates the temperature sensed by the device100. In one embodiment, the n-bit counter generates a 16-bit count.Alternate embodiments generate other count lengths.

The counter 101 is clocked by a signal generated by a temperaturecompensated refresh oscillator 103. The clock signal has a variableperiod such as the lower waveform in FIG. 2. The period of this signalincreases as the temperature of the oscillator 103 decreases and theperiod decreases as the temperature of the oscillator 103 increases.

In one embodiment, the oscillator 103 may output a squarewave that has aperiod of 9 microseconds when the oscillator is at its warmest value. Atits coldest value, the oscillator 103 may output a 500 microsecondsignal. These periods are for purposes of illustration only. The presentinvention is not limited to any one period for any temperature ortemperature range.

The counter 101 is enabled by a fixed rate oscillator 105 that istemperature invariant. The fixed rate oscillator 105 generates a sensetime signal that has a fixed width such as the signal illustrated in thetop waveform of FIG. 2. In one embodiment, this width is 5 milliseconds.Alternate embodiments use other widths.

The width of the sense time signal is determined by the frequency rangeof the variable rate, temperature compensated oscillator 103. Thegreater the quantity of cycles of the variable rate signal that canoccur during a sense time, the more accurate the resulting temperatureindication from the counter 101.

The sense time signal is used as a known temperature sense timeinterval. When it is at a logical high value, the counter 101 is allowedto count. This is considered the sense time interval. When the fixedperiod signal is at a logical low value, the counter 101 is inhibited.

An oscillator read logic block 107 is coupled to both the fixedoscillator 105 and the n-bit counter 101. The read logic block 107generates a reset pulse prior to each sense time interval. This pulseresets the counter to a default status, such as zero, so that a newtemperature value can be determined each time.

The read logic block 107 also triggers the fixed oscillator 105 tooutput its logical high, sense time signal. Since a silicon device doesnot change temperature rapidly, sense time signal does not have to begenerated very often. In one embodiment, the time between triggering thesense time signal is in the range of 500 milliseconds to 1 second.Alternate embodiments may use different times.

The elapsed time between successive, fixed read time intervals reducesoverall current drawn by the system. The circuit is “awakened”periodically, makes a measurement during the fixed read time intervalthen shuts down until the next fixed read time interval. This lowers theaverage current drawn by the system.

In operation, the n-bit counter 101 is first reset to zero by theoscillator read logic 107 prior to the start of a read time interval.The fixed period signal goes high to enable the counter 101 so that theclock input (i.e., variable rate signal) causes the counter to count upat a rate that varies with temperature. After the fixed oscillatorsignal goes low to indicate an end of the sense time interval andinhibit any further counting during the sense cycle. The resultingcounter output indicates the temperature of the integrated circuit inwhich the oscillator circuit is embedded. A relatively high countindicates a higher sensed temperature. A relatively low count indicatesa lower sensed temperature.

In one embodiment, the count value output from the counter 101 is a16-bit value. This value can be read by a controller or other circuitrywithin the integrated circuit and used for various operations requiringan operating temperature. The 16-bit counter value results in being ableto differentiate between a greater number of temperatures in atemperature range for the integrated circuit. The present invention,however, is not limited to any one counter bit length.

FIG. 2 illustrates a timing diagram of signals generated by thetemperature sensing device of FIG. 1. The upper waveform illustrates thetemperature invariant, sense time signal with a width measured inmilliseconds. The lower waveform illustrates the output of thetemperature compensated refresh oscillator. The periodicity of thissignal varies as the temperature of the circuit of FIG. 1 changes.

The left portion of the lower waveform indicates the period of thetemperature compensated refresh oscillator signal when the temperatureof the temperature sensing device is warmer. This portion of the signalhas a greater number of pulses during the high period of the fixed readtime interval signal. In the illustrated embodiment, the period of thisside of the signal is 9 microseconds.

The right portion of the lower waveform indicates the period of thetemperature compensated refresh oscillator signal when the temperatureof the temperature sensing device is colder. This portion of the signalhas the lesser number of pulses during the high period of the fixed readtime interval signal. In this embodiment, the period is 500microseconds.

The waveforms of FIG. 2 are for purposes of illustration only. They arenot to scale and do not limit the oscillators of the present inventionto any one set of frequencies.

FIG. 3 illustrates a graphical plot of the temperature of an integratedcircuit into which the temperature sensing device of the presentinvention is embedded versus the period of the variable rate signaloutput from the temperature compensated refresh oscillator. This graphshows that as the temperature of the part increases, the period (inmicroseconds) decreases.

FIG. 4 illustrates one embodiment of an implementation of thetemperature sensing 100 device of the present invention. In thisembodiment, the temperature sensing device 100 is embedded in a memorydevice 400. Examples of such a memory devices can be dynamic randomaccess memories (DRAM), pseudo static RAMs (PSRAM), or flash memories.Alternate embodiments use other types of memory.

In a memory device that uses the temperature to determine refresh rate,such as a DRAM, the memory's refresh controller or memory controller 403can read the count value and use it to determine the refresh rate forthe memory array 405.

The controller 403 can use the count from the temperature sensing device100 in various ways. In one embodiment, the controller contains or hasaccess to a table that lists various count values and theirrepresentative temperatures. For example, a count of FFFFH may indicatethe maximum temperature of the part (e.g., 85° C.). The controller canthen increase the refresh rate of the memory array 405. If the countindicated a colder temperature, the controller can decrease the refreshrate of the memory array 405.

In another embodiment, the controller contains or has access to a tableof count value thresholds, each threshold indicating a different refreshrate. For example, a count value between 0000H and 00AAH may indicate afirst refresh rate. A count value between 00BBH and 0100H may indicate aslightly higher refresh rate since the higher count indicates a highertemperature.

FIG. 5 illustrates a block diagram of another implementation of thetemperature sensing device 100 of the present invention. This embodimentis a battery powered electronic device such as a cellular telephone.

typical cellular telephones use an external discrete temperature sensorto monitor the temperature of the battery while it is charging. Thesensor allows the charger to vary the charging current to keep thebattery voltage below a predetermined threshold so that the telephonedoes not overheat.

Since cellular telephones are typically small devices, the heat from thebattery will heat the circuit elements of the telephone including amemory device that includes the temperature sensing device 100 of thepresent invention. Accordingly, the temperature of the memory device canbe used to infer the battery temperature. Taking a backgroundtemperature measurement at ambient prior to the start of the chargingprocess can compensate for the effect of ambient temperaturedifferences. The temperature acceleration is then monitored as thecharging process proceeds. If the operating current of the memory deviceis low (i.e., 10's of milliamps), the effects of die heating from theactive current consumption are small and can be compensated for.

The embodiment of FIG. 5 is comprised of a memory device 400 with anembedded temperature sensing device 100. One example of such a memorydevice is illustrated above with reference to FIG. 4.

The memory device is coupled to a microprocessor 501 or other type ofcontroller circuit that controls the operation of the cellulartelephone. A display 503 is used by the microprocessor 501 to displayinformation to the telephone user. The display may be liquid crystaldisplay (LCD), light emitting diode (LED) display, or some other type ofdisplay.

A keypad or keyboard 505 is used to enter data such as names andtelephone numbers. The keypad 505 can also be used to communicateinstructions to the microprocessor 501.

A battery 507 powers the telephone. The battery can be of any technologysuch as lithium ion, nickel cadmium, or other types.

FIG. 6 illustrates a flow chart of one embodiment of a memory read cycleenabling an external system to read the temperature sensing device ofthe present invention that is embedded in a memory device. The methodreads the device as if it is an internal register and therefore uses anaddress that is reserved for system use).

The method performs two asynchronous read cycles to the system address601. In one embodiment, this address is the highest address in thememory address range. Two asynchronous write cycles are then performedto this address 603. The write data pattern indicates which internalregister is to be read from. For example, if 02H is assigned to thetemperature sensing device, this data pattern would be written on thetwo write cycles. The 16-bit counter value that represents thetemperature is now available on the data bus 605.

The method of FIG. 6 illustrates only one embodiment for accessing thecounter value that represents the temperature of the integrated circuit.Alternate embodiments might include performing only one read and writecycle with the appropriate register address in the data field.

FIG. 7 illustrates a flow chart of one embodiment of a temperaturesensing method of the present invention. This method could be used in acellular telephone such as the embodiment illustrated above in FIG. 5 orin any other electronic device that uses a battery.

In this embodiment, an initial reading of the ambient temperature isdone prior to charging the battery 701. The charging process is theninitiated 703. The corrected temperature (corrected for ambienttemperature) is monitored during the charging process 705. Themonitoring can be accomplished either periodically or at randomintervals. When the temperature acceleration is too great, indicatingthat the temperature will reach a dangerous temperature threshold 707,the charging current is reduced 709.

The corrected temperature monitoring for this method of the presentinvention is accomplished by reading the temperature sensing device ofthe present invention as discussed previously. The initially measuredambient temperature is then subtracted from the sensed temperature togenerate the corrected temperature that is used to monitor thetemperature acceleration.

CONCLUSION

The embodiments of the present invention provide a temperature sensingdevice that can be embedded in an integrated circuit such as a memorydevice. The temperature sensing device generates a counter value thatindicates the temperature of the memory device. This temperature canthen be read by a modified memory read cycle that enables an externalsystem to access the temperature indication.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe invention will be apparent to those of ordinary skill in the art.Accordingly, this application is intended to cover any adaptations orvariations of the invention. It is manifestly intended that thisinvention be limited only by the following claims and equivalentsthereof.

1. A dynamic random access memory (DRAM) comprising: a memory arraycomprising a plurality of memory cells; a memory controller circuitcoupled to the memory array for generating refresh signals at a refreshrate determined by a temperature signal; and temperature sensing device,coupled to the memory controller, for generating the temperature signal,the device comprising: a temperature variant oscillator that generates avariable rate signal having a frequency that varies in response to atemperature of the DRAM; a temperature invariant oscillator thatgenerates a fixed rate signal indicating a sense cycle; and a counterthat generates the temperature signal as an n-bit count in response tothe variable rate signal and the fixed rate signal.
 2. The DRAM of claim1 wherein the n-bit count value is 16 bits.
 3. The DRAM of claim 1wherein the fixed rate signal enables the counter when a temperaturesense period is desired and the variable rate signal clocks the counter.4. The DRAM of claim 1 wherein the counter is reset prior to each sensecycle.
 5. The DRAM of claim 1 wherein a warmer temperature is indicatedby a larger count value and a colder temperature is indicated by asmaller count value.
 6. The DRAM of claim 1 wherein the refresh rate isincreased for warmer temperatures and decreased for colder temperatures.7. A dynamic random access memory (DRAM) comprising: a memory arraycomprising a plurality of memory cells; a memory controller circuitcoupled to the memory array for generating refresh signals at a refreshrate determined by a temperature signal; and temperature sensing device,coupled to the memory controller, for generating the temperature signal,the device comprising: a temperature variant oscillator that generates avariable rate signal having a frequency that varies in response to atemperature of the device; a temperature invariant oscillator thatgenerates a fixed rate signal indicating a sense cycle; a counter thatgenerates the temperature signals as an n-bit count value in response tothe variable rate signal and the fixed rate signal; and an oscillatorread logic, coupled to the temperature invariant oscillator and thecounter, for resetting the counter to a default status and triggeringthe temperature invariant oscillator to generate the fixed rate signal.8. The DRAM of claim 7 wherein the default status is zero.
 9. The DRAMof claim 7 wherein the fixed rate signal is a logically high signal andthe variable rate signal comprises logically high pulses to clock thecounter.
 10. The DRAM of claim 7 wherein the fixed rate signal isgenerated at predetermined intervals in a range of 500 milliseconds to 1second.
 11. The DRAM of claim 7 wherein the fixed rate signal has awidth measured in milliseconds.
 12. A dynamic random access memory(DRAM) comprising: a memory array for storing data; a memory controllercoupled to the memory array that generates refresh signals at a refreshrate responsive to a temperature signal; and a temperature sensingdevice, coupled to the memory controller, for generating the temperaturesignal in response to a temperature of the memory, the temperaturesensing device comprising: a temperature variant oscillator thatgenerates a variable rate signal having a frequency that varies inresponse to a temperature of the memory device; a temperature invariantoscillator that generates a fixed rate signal indicating a sense cycle;and a counter that generates the temperature signal as an n-bit countvalue in response to the variable rate signal and the fixed rate signal.13. The DRAM of claim 12 wherein the refresh rate is increased as thetemperature of the memory increases and decreased as the temperature ofthe memory decreases.